You could try thinking simpler. Drivers can cause this. Try starting in safe mode which will exclude the running of all but the simplest of drivers. You will lose the use of certain things, but it may just work. Video drivers can be bad for this and sometimes it is worth loading an older driver (assuming your drivers are the latest). You could also try creating a log on startup which will show you the last driver/service to load.
Also you could remove all unecessary cards, drives, usb devices, extra memory modules and run it as a basic system. If it works, switch off (Run down), replace any cards etc ONE BY ONE and restart. You may just find the offending item.
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